This invention relates to a feeding mechanism and more particularly to a mechanism for feeding flat objects such as bags, file folders, x-ray jackets, heavy paper etc. by use of a vacuum assisted feeding device.
Many types of devices are known for feeding flat objects such as sheets of paper, plates, bags, etc. in which a rotating cylinder, supplied with holes through a surface of the cylinder and being connected to vacuum suction, is used to separate a single item from a stack of items for transport. Oftentimes valves and other arrangements are utilized to turn the suction on and off as the cylinder rotates and/or the cylinder is periodically stopped from rotating in order to provide a gripping force and to remove the gripping force as the item is moved by the cylinder.
For example, in U.S. Pat. No. 5,088,717 a cylinder unit is provided having an outside pipe member with a plurality of small through holes. The outer surface of the outer pipe member is covered by a synthetic rubber. An internal, middle pipe member has openings through an angle .alpha. said in the range of 10.degree.-80.degree. . A third internalmost pipe member is provided with openings through an angle .beta. in the range of 10.degree.-80.degree. . By selectively rotating the concentric cylindrical member members, suction is alternatively provided or not provided at the outermost pipe. Also this patent teaches to not rotate the cylinders in a continuous manner, but in fact to stop the rotation in order to draw an item by suction into engagement with the stationary cylinder before suction is applied and rotation resumes. Further, an air blast device is used to remove a part of the weight of the stack of items from the item in engagement with the rotating cylinder.
U.S. Pat. No. 3,998,449 discloses a rotatable cylinder which has vacuum ports therethrough and also has a protuberance in the form of an elongated bar which extends above the cylindrical surface for engaging and dislodging an item from a stack. Again, the vacuum is selectively applied and removed from the vacuum ports such that suction is applied at the outer surface of the cylinder only intermittently.
U.S. Pat. No. 4,184,670 also discloses intermittent provision of suction as well as intermittent rotation of the cylinder and U.S. Pat. No. 4,758,126 also discloses intermittent provision of suction.
U.S. Pat. No. 5,255,905 discloses the use of a stationary vacuum device which is intermittently operated in connection with a conveyor. Air knife jets are also used to separate documents in a stack from which the bottommost document is being withdrawn by the conveyor.
U.S. Pat. No. 5,125,638 discloses the use of pivotally mounted sucker members carried on a rotatable cylinder which operate intermittently to engage a sheet and draw it toward the cylinder. A pivoting presser wheel presses the sheet against the cylinder and the vacuum at the sucker member is released causing the sheet to be carried along between the presser roller and a conveyor belt.